[Increased expression of HMGB1 and TLR4 in intestinal tissues and intestinal immune dysfunction in severely burned rats].

Objective To investigate the expressions of high mobility group box 1 (HMGB1) and Toll-like receptor 4 (TLR4) in the intestinal tract of severely burned rats and their relationship with intestinal immune function. Methods Forty male SD rats were randomly divided into control group (n=10) and severe burn group (n=30). 60% of the rats' body (the back and ventral side) was burned in the severe burn group, and only anesthesia was performed in normal control group. Rats were sacrificed at 6, 12 and 18 hours after injury in the burn group, while sacrificed immediately after anesthesia in control group. The protein levels of HMGB1 and TLR4 in the intestinal tissue were detected by Western blotting. The purity of total T cells (CD3+ T), as well as the ratio of Th1 to Th2 cell subsets, was measured by flow cytometry. ELISA was performed to detect the concentrations of IFN-γ, IL-4 and IL-10. Results Compared with the control group, the protein expressions of HMGB1 and TLR4 in the severe burn group were significantly higher than that in the control group at 6, 12 and 18 hours after injury, in a time-dependent manner. A positive correlation between HMGB1 and TLR4 protein expressions in the severe burn group was observed. The ratio of Th1 to total T cells was significantly raised at 6, 12 and 18 hours after burn injury, and the ratio of Th2 to total T cells decreased, and the ratio of Th1/Th2 significantly increased. Th1 cell percentage was positively correlated with HMGB1 and TLR4, while Th2 cell percentage was negatively correlated with HMGB1 and TLR4. Compared with the control group, the levels of IFN-γ and IL-4 in the intestinal tract were significantly elevated at 6, 12 and 18 hours after severe burn injury, while the level of IL-10 was significantly reduced. With the increase of postburn time, the levels of IFN-γ and IL-4 gradually increased, while the level of IL-10 gradually decreased. Conclusion HMGB1 was recruited in the intestinal tissues to activate TLR4 signaling pathway after severe burn, further activates the downstream signal transcripts and releases a series of inflammatory cytokines to induce inflammatory response, which is involved in Th1 and Th2 cell mediated immune function obstacle of rats.